The work proposed here will investigate the roles played in the osmodetection process by the neurons and glial cells in and around three magnocellular nuclei paraventricular and supraoptic nuclei and the nucleus circularis all of the hypothalamus. In addition, osmosensitive cells, in other nearby locations, that may be presynaptic to the neurons of the three magnocellular nuclei will be investigated. The approaches to be used in these studies include light and electron microscopy, electrophysiology of brain slices and immunocytochemistry.